The development and maintenance of the gametogenic process is largely dictated by interactions between the somatic and germ cells of the seminiferous tubule. However, the signals exchanged between somatic Sertoli cells and germ cells and the intracellular transduction pathways activated by these interactions are poorly understood. In this proposal, experiments are designed to understand how the cAMP-dependent pathway is modulated by the gonadotropin FSH and to define the role of this pathway in the differentiation and function of the Sertoli cell during the spermatogenic process. During the past years we have developed recombinant and immunological probes for gonadal cyclic nucleotide phosphodiesterases, the enzymes that degrade the second messenger cAMP. We have also provided evidence that these enzymes are regulated by the gonadotropin FSH and are involved in the control of Sertoli cell responsiveness. Here it is proposed to study the expression, the regulation and the role of the cAMP-PDEs of the Sertoli cell. The expression and localization of the two cAMP-PDEs will be monitored by biochemical and immunological approaches, and by transfection of the two cAMP-PDEs in the Sertoli cell and in another gonadotropin-responsive system that we have established (MA-10 Leydig cell tumor line). By these approaches and by measuring responses of the transfected cells, it will be assessed if the two forms have different or identical functions in the Sertoli cell. The structure of the rat genes encoding the two cAMP-PDEs and the function of the flanking regions will be determined. To understand the mechanism by which FSH and other gonadotropic hormones regulate these enzymes, hormonal regulation of the rates of transcription of the PDE genes and the rates of protein synthesis and activation will be studied in cultured Sertoli cells. Following the finding that expression of the cAMP-PDEs increases together with the Sertoli cell maturation that occurs during testis development, we will determine the mechanism that leads to this age-dependent activation, which will help to understand the mechanism that governs Sertoli cell maturation. The significance of the cAMP-PDE induction during development will be assessed by studying its role in the changes in Sertoli cell responsiveness that occur during development. Finally, cAMP-PDE expression will be investigated in the Sertoli cell during the seminiferous tubule cycle, and it will be determined if fluctuations in Sertoli cell responsiveness are due to a germ cell-dependent regulation of these cAMP-PDEs. These studies will improve the understanding of the mechanisms of gonadotropin action and will provide insight into the mechanisms controlling gametogenesis.